the previous poster was correct that 512MB of RAM is the "sweet spot" for Windows XP to run well with a couple of programs open. Microsoft says XP will run with 128MB of RAM, but their idean of "run" and ours are totally different. 128MB of RAM will make it run like molasses. 256MB is the real minimum for rudimentary useage. 512MB is best. And XP really hums if you have a video card with separate RAM -- not the "shared" system RAM only which regrettably is becoming more common.
However, the original question was the inordinate start up time of Word and Excel. Too little RAM would be evident even in starting up the browser -- so it's not just general slowness, but one set of applications in particular: Microsoft Office. In that case, it's probably Norton causing that particular slowness, according to other people's experience in other user groups. Disconnect from the Internet, temporarily disable your Norton, see if the start up times dramatically improve. If so, change out your anti-virus application with another trusted brand. There are some that strive for superior protection AND wise use of system resources; read reviews and find them.